High temperatures, pressures and corrosive chemical environments are all known to cause advanced wear and erosion of metals. While the present invention is directed in part to the general filed of chemical dispersions and coatings, in one particular application, the repeated high temperatures, pressures and chemical environments found in the interiors of gun barrels cause wear on these gun barrels, and eventually contribute to the limited usable lifetimes of such.
When a gun is fired the propellant generates temperatures as high as 2200° C. to 3500° C. and pressures between 20,000 and 80,000 psi. These extreme conditions lead to wear of gun barrels via mechanisms including mechanical stress from the heat and pressure, chemical interaction of the barrel with combustion gases, and abrasion from unburnt particles. This wear leads to enlargement of the gun bore or damage to its surface, which reduces muzzle velocity, range, and accuracy. Consequently, firearm lifetime is limited by barrel erosion, and the adoption of more powerful propellants cannot be realized because of the unreasonably low durability caused by advanced propellants. Further, the use of propellants that are stoichiometrically balanced would eliminate secondary muzzle flash and the associated signature of this phenomenon. However, the high temperatures produced by fuel and oxidant balanced propellants would erode the barrel very quickly, thus preventing their practical use.
Propellant additives can be used to reduce gun barrel wear and could permit the use of higher performance propellants. For example, small amounts of ceramic oxides (usually 1% or less), such as titania and silica, have been shown to be effective additives to propellants for reducing gun barrel wear. These additives have been shown to deposit on the walls of the barrel after firing, creating a coating that is more resistant to chemical attack, oxidation, and wear. Boron nitride is of particular interest because of its oxidation resistance. Hexagonal boron nitride has the same structure as graphite and is an excellent lubricant, but unlike graphite, boron nitride does not readily oxidize in air. Further, boron-doping of steel can improve its hardness. However, scalable and economical production of boron nitride nanoparticles with a narrow distribution of small diameters necessary to be effective additives (less than approximately 200 nm) has yet to be realized. Typical approaches for producing nano-BN involve beginning with larger particles and milling them to smaller sizes. The resulting product typically cannot be dispersed without agglomerations, does not have a narrow distribution of small particles, and it is often oxidized as a result of the milling process.